Method of making iron powder



United States Patent 'NIETHOD OF lvlAKlNG RON POWDER Hubert Hoff and Wilhelm vor dem Esche, Dortmund,

and Heinz Lessing, Essen-Altenessen, Germany, assignors to Westfalenhutte Dortmund Aktiengeselischaft, Dortmund, Germany, a German company No Drawing. Application June 19, 1951, Serial No. 232,472

Claims priority, application Germany June 20, 1950 2 Claims. (31. 7s .s

This invention relates to the manufacture of sintered iron powder and has for its object, by the employment of a novel starting material, to produce a sintered iron powder which, while at least equal in quality to other known sintered iron powders, possesses the advantage of a considerably lower cost price. By this means the most serious obstacle which, despite their many advantages, has hitherto limited the use of the products of powder metallurgy is removed.

Up to the present time the production of sintered iron powders which, dependent on the purposes for which they are to be used, must have grain sizes up to about 0.4-0.5 mm., has been carried out mechanically or chemically in accordance with different standard processes. One of these processes consists in reducing compact iron to the necessary range of grain sizes in a purely mechanical manner in high-speed beater mills. Other processes utilise iron in the fluid state which is brought by suitable measures into the required finely divided form. This is .efiected, for example, by causing a thin stream of iron, after granulation by a jet of water under pressure, to impinge on a centrifuging disc provided with beater elements. Alternatively the stream of iron particles may be caused to impinge on a jet of steam or compressed air.

In the chemical process for the production of sintered iron powder, the starting materials are oxidic iron compounds, such as rolling mill sinter, hammer scale, Scandinavian iron ore concentrates and the like, which have to be reduced. When quite pure iron powder, such as the so-called carbonyl iron, is to be produced, iron pentacarbonyl having the formula Fe(CO)s is used as the starting material.

Without further explanation it will be appreciated that sintered powders produced in this manner are very expensive, mainly due to the costs of processing. In addition, the known manufacturing processes often result in a sintered powder in which the distribution of the grain sizes and the shape of the particles is unsuitable for the pressing operation.

The process according to the present invention makes use of a waste product, namely furnace dust from blast furnace installations, as the starting material for the production of sintered iron powder. In the condition in which it normally occurs this furnace dust contains up to 50% Fe, substantially in the form of magnetic F6304.

The following table gives an example of a furnace dust composition according to grain size, this being an average obtained from numerous separate tests:

2,721,134 Patented Oct. 18, 1955 ice 2 Grain size: Deposit, percent Greater than V 0.5 mm 0.0 0.3 mm l0 0.2mm 15 0.15 mm 25' 0.12 m '12 0.10 mm 13 0.088 mm .6 0.075 -mm 6 v Smaller than- Total 100 This grain size distribution is suitable without modification for the manufacture of sinter powder.

The use of furnace dust as the starting material for the production of sintered iron powder has already been proposed per se, but such proposals, according to which the furnace dust is subjected to a reduction treatment and used directly, have not been put into commercial practice apparently for the reason that the sintered powder produced in accordance with these proposals did not satisfy the requirements. The present invention is based on the recognition that special measures have to be taken in order to obtain from the furnace dust a product which can be used as the basis of the sinter powder.

Accordingly, the process according to the invention comprises subjecting the furnace dust being formed to a concentration treatment by which only the comparatively small percentage of iron and iron oxide particles which, as already shown, is suitable for being worked up to sinter powder, is eliminated from the total mixture and only this percentage is then subjected to the reducing process.

The aforesaid concentration may be effected by magnetic separation, conveniently in an alternating current field, and may, if desired, be followed by a wet mechanical treatment in accordance with processes usual in the preparation of dressed ores, for example, on high speed percussion frames. The concentration process may be repeated one or more times if necessary or desirable. The concentates thus formed with an Fe content of up to more than (97% FesOi) are then subjected to a reducing treatment in the course of an annealing process by hydrogen or other reducing gases, such as the blast furnace gas which is available on the spot, or other reducing agents.

By suitable adjustment of the frequency and of the current intensity, it is possible in this manner to extract from the furnace dust the iron oxide particles not connected with the gangue, namely just those particles having a grain size which is most suitable for the sinter powder. Furnace dust occurs in such qantities that it is possible to take only the serviceable particles by this preparation treatment and discard the remainder. The fact that, as a result of this action, what seems to be in itself an unfavourable proportion of the amount of furnace dust undergoing the treatment is produced as usable sinter powder is not important, because the processes of preparation can be inexpensively operated and the necessary mechanical equipment installed in the customary path of 'without'the granulation of the starting material being 3 4, V V g travel of the dust in such manner that no high transport ance with the known reduction processes; in fact so fa costs are incurred. as powders produced by mechanical disintegration are One embodiment of the concentrating and reducing concerned they are superior in regard to grain size comprocess will now be described by way of example, it beposition and particle shape, and moreover they can be ing understood that instead of the preparation steps de- 5 produced at'a fraction of the cost of these known sinter scribed other processes of a similar nature may be empowders. ployed. For example, the magnetic separation followed The pressed particles produced from these powders by wet preparation can be replaced by repeated magnetic by the use of pressures of 3-10 t./cm. and subsequent separation with or without intermediate annealing, etc. sintering in a hydrogen atmosphere at 1050* C. have sub- A furnace dust of 51.26% Fe content was subjected to stantially the same properties as sintered iron products magnetic separation in an alternating current field. There made from the sinter powders produced by the substanwas obtained: tially more expensive processes already discussed.

The possibility afforded by the present process of con- Fumaee dust in the condition in vetting a technically waste product in an extremely simple Magnet cmcenmte'percent manner and without appreciable cost into a valuable which it occurs, percent sintered iron powder opens entirely new avenues in the 10% clean iron and clean iron oxide particles of grain size less than 0.5 mm., and subjecting such particles to a reduction treatment.

2. A process for manufacturing iron powder suit- 1 About 70% F8104.

2 About 97% o able for sintering from blast furnace flue dust, which conthis examplevlo kg. of sinter powder were obtained sists 1n magnetically treating the flue dust to separate from 100 of furnace dust, and 70% of this powder h therefrom clean iron oxide particles of grain size less azgrain size between 0.12 and 0.3 mm. There were no than 0.5 mm., and subjecting such particles to reducgrains of a size above 0.5 mm. for the reason that these were not even included in the furnace dust. The peronly shghfly lowered Consequmfly the adaptzfblmy centage of fine particles below 0.12 amounted to 30%. V for use the mtmductlon to the. blast furnace Is not The residual furnace dust had in this case an Fe content substantlany changed' of 49%. A

1 If it is decided, for example, that the optimum value References (med in the file of this patent of grain size, which in the example is 25% with a grain 40 UNITED STATES PATENTS size of 0.15 mm., should be modified by 0.2 and 0.3 mm-, 156,093 La Rue Oct. 20, 1874 this can readily be achieved by varying the frequency 1,517,402 Constant Dec. 2, 1924 and current intensity. The yield in this case is a litt e 2,296,522 Hartley Sept. 22, 1942 less; 2,307,064 Patterson Jan. 5, 1943 By. means of a hydrogen reduction at 800 C., for 2,368,489 Patterson Jan. 30, 1945 example, the oxidic'iron is converted to the metallic form 2,468,586 Braund Apr. 26, 1949' modified. All annealing processes are carried out at OTHER REFERENCES 7 temperatures below which sintering of the particles can Concentration 0f Blast Furnace Flue Busts," y

1 55.32 2 8- 3 field of powder metallurgy and renders the use of sintered 54 products possible in numerous fields in which-they have $2 3 not hitherto been employed on account of the high price 45 "53;; 20 of the sinter powder.

I 1}.23 8- 3 We claim: a

1. A process for manufacturing iron powder suitable 4 g for sintering from blast furnace flue dust, which consists in magnetically treating blast furnace flue dust con- 0.42 taining approximately 50% iron to separate therefrom tion treatment so that the iron content of the remainder is occur and in such manner that the powder character of 50 Shelton and Lamb, Published in the Iron June the material is maintained. 11, 1942, P g 59- I The process described yields results which are at least equal to the sintered iron powders produced in accord- 

1. A PROCESS FOR MANUFACTURING IRON POWDER SUITABLE FOR SINTERING FROM BLAST FURNACE FLUE DUST, WHICH CONSISTS IN MAGNETICALLY TREATING BLAST FURNACE FLUE DUST CONTAINING APPROXIMATELY 50% IRON TO SEPARATE THEREFROM 10% CLEAN IRON AND CLEAN IRON OXIDE PARTICLES OF GRAIN SIZE LESS THAN 0.5 MM., AND SUBJECTING SUCH PARTICLES TO A REDUCTION TREATMENT. 